1) Field of the Invention
This invention relates generally to fabrication of magnetoresistive (MR) sensors employed within data storage and retrieval. More particularly, the present invention related to enhanced magnetoresistive (MR) spin valve filtering giant magnetoresistance (GMR) sensor elements.
2) Description of the Prior Art
In recent years, improvement in sensitivity of magnetic sensors and increase in density of magnetic recording are advancing. Concomitantly, development of magnetoresistance effect magnetic sensors (hereinafter abbreviated to MR sensors) and magnetoresistance effect magnetic heads (hereinafter abbreviated to MR heads) is making rapid progress. Each of the MR sensors and the MR heads is operable to read an external magnetic field signal as an electric resistance variation in a sensor in response to the external magnetic field. In these MR sensors and MR heads, reproduction outputs do not depend upon relative speeds with respect to recording media. This leads to high sensitivity of the MR sensors and high output levels of the MR head in high-density magnetic recording.
Recently, proposal is made of a magnetoresistance effect film which comprises at least two ferromagnetic layers or thin films stacked one over the other with a nonmagnetic layer or thin film interposed therebetween, and an antiferromagnetic layer or thin film underlying a first one of the ferromagnetic thin films so that the first ferromagnetic thin film is provided with antimagnetic force, that is, constrained by exchange anisotropy or exchange biasing.
A so-called soft magnetic material or a high permeability magnetic material is usually used for the ferromagnetic layers. The term “nonmagnetic” is usually used to mean “paramagnetic” and/or “diamagnetic”.
When an external magnetic field is applied to the magnetoresistance effect film, the direction of magnetization of the other second one of the ferromagnetic thin films is rotated with respect to that of the first ferromagnetic film. Thus, change in resistance takes place.
Disclosure is also made of a conventional magnetic read transducer, called an MR sensor or an MR head, which can read data from a magnetic surface with high linear density. The MR sensor detects a magnetic field signal through change in resistance as a function of the intensity and the direction of magnetic flux detected by a reading element. The above-mentioned conventional MR sensor is operated on the basis of an anisotropic magnetoresistance (AMR) effect. Specifically, one component of the resistance of the reading element changes in proportion to the square of the cosine of the angle between the magnetization direction and the direction of the sense current flowing through the element.
More recently, disclosure is made of a further remarkable magnetoresistance effect. Specifically, change in resistance of a stacked-type magnetic sensor results from spin-dependent transmission of conduction electrons between ferromagnetic layers with a nonmagnetic layer interposed therebetween and from interfacial spin-dependent scattering accompanying the spin-dependent transmission. Such magnetoresistance effect is called by various names such as “a giant magnetoresistance effect” and “a spin-valve effect”. Such magnetoresistance effect sensor made of an appropriate material has improved sensitivity and exhibits large rate of change in resistance. In the MR sensor of the type described, in-plane resistance between a pair of the ferromagnetic layers separated by the nonmagnetic layer changes in proportion to the cosine of the angle between magnetization directions in the two ferromagnetic layers.
It has been recognized that the electronic and structural natures of interfaces are key elements in the understanding of mechanism behind GMR effects. Improved electron reflectivity in the GMR/Insulator interface was found to improve significantly the GMR ratio.
There is a need to improve the electron reflectivity in the GMR/Insulator interface. This invention is directed towards this end.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 5,843,589 (Hoshiya et al.), and U.S. Pat. No. 5,766,743 (Fujikata et al.).